Your facts seem to indicate that a buy-sell agreement must be in writing to be effective. That is incorrect. It appears that the other shareholder will claim that there was an oral agreement on a buy-sell. Now, that will be a very difficult claim if there are no facts to support this, but this could be a claim.
That said, based on your limited facts, you should be able to sell your shares. Your shares are your property and absent a written or oral agreement that would restrict your right to sell, you are free to do what you want. I strongly recommend that you speak with a NY business attorney to cover all bases.
This answer is for informational purposes only and is not legal advice regarding your question and does not establish an attorney-client relationship.
Generally, unless conspicuously noted on the share certificate, restrictions on transfers are not enforceable against a shareholder who has no way of knowing about them. New York considers shares as personal property and forbids unreasonable restrictions on their sale. Additionally, where a selling shareholder is required to obtain consent of other shareholders, New York courts have found such a restriction to be not enforceable. However there are exceptions in tenant-shareholder cooperatives and professional service corporations. So please consult a business attorney. He will be able to take a look at the corporate documents and tell you if you are in fact bound to a "First Option" restriction or a "Consent" restriction. Hope this helps.
This answer is general information only. No legal advice is given in this answer. No attorney-client relationship is established based on this answer. To receive accurate legal advice, please follow up with an attorney.
This is a most unusual scenario.
I am a NY business lawyer and before I would answer this conclusively, I would want to just double check to ensure that there are no statutes that speak to this situation regards to close corps. I do not believe that to be the case, but an issue like this is not that common. For example in CA, where we have several clients, there is a slightly different regime regards to close corps.
So unless there is some written provision that states otherwise, you cannot prevent a shareholder from selling their shares. That is their asset and is no different than preventing them from selling their other personal property.
What makes this so unusual is that in a 50/50 context it is near impossible for one partner to sell their shares to some third party that is a stranger to the business. That is, would you want to buy into a business where 50% is owned by someone who does not want you there? That is quite problematic.
I suggest you discuss this over in more detail with a lawyer so all the facts and circumstances are understood.
Most of us here, including myself, offer a free phone consult so you should take advantage of that.
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